The invention relates to a method for modulating a basic clock signal for digital circuits and a clock modulator for modulating a basic clock signal for digital circuits. Modulation of the basic clock signal is used in order to give interference caused by the basic clock signal a broader-band configuration and thus to distribute the interference energy between additional frequencies and hence to reduce the absolute heights of the resulting interference spikes.
The applicant's patent application (DE 198 02 065.A1), which is a prior application, corresponding to U.S. Pat. No. 6,393,078, discloses a method for modulating a basic clock signal for digital circuits and a corresponding clock modulator in which the distances between adjacent switching edges are altered, the respective distance being achieved by virtue of the fact that the basic clock signal is conducted via a changing number of delay units and the distances between the adjacent switching edges are altered in this way.
This method and this clock modulator have the disadvantage that frequency modulation is achieved which, although it greatly attenuates the fundamental frequency, does not readily correspond to the fundamental frequency in terms of its time average,